The Stairs first appeared in the 2015 Halloween Event. Despite appearing to be an innocuous set of stairs leading to nowhere, many players have found out the hard way that walking up them leads into the void.
The Stairs are a simple set of quartz stairs in the middle of the forest in Halloween Town. Climbing to the top of the stairs will instantly kill the player.
Many NPC's in the event warn about the danger of the stairs, but do so vaguely like in a cliche horror movie.
Citizens of Halloween Town fear this mysterious staircase that seems to appear and disappear at will in the forest. Going near them causes disaster to strike, often resulting in gruesome deaths. As a consequence, the townsfolk try not to talk about the stairs. They believe that speaking about them will cause others to investigate, bringing death upon them all.
"We don't talk about the stairs..."
- Nate has stated that the stairs are actually a reference to his favourite /r/nosleep series